Cam has a number of parameters and it needs to be matched to the rest of your build. Cam has a duration value that tells you how many degrees the valve stays open, lift which is how high the valve is lifted off the seat. Lift is also affected by rocker ratio and valve geometry. Next parameter is lobe separation angle and is the angle between the intake and exhaust lobe centerlines. Lift value should be based off intake valve size. Duration and lsa determine where peak power will occur although head flow and compression can alter where peak power occurs.

Carb size affects how much airflow can go thru it., and needs to be matched to the engines airflow requirements. Too small and you limit power, too big can kill off low rpm power and responsiveness of the engine.

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Carb size affects how much airflow can go thru it., and needs to be matched to the engines airflow requirements. Too small and you limit power, too big can kill off low rpm power and responsiveness of the engine.

Cam has a number of parameters and it needs to be matched to the rest of your build. Cam has a duration value that tells you how many degrees the valve stays open, lift which is how high the valve is lifted off the seat. Lift is also affected by rocker ratio and valve geometry. Next parameter is lobe separation angle and is the angle between the intake and exhaust lobe centerlines. Lift value should be based off intake valve size. Duration and lsa determine where peak power will occur although head flow and compression can alter where peak power occurs.

New Member

Carb size affects how much airflow can go thru it., and needs to be matched to the engines airflow requirements. Too small and you limit power, too big can kill off low rpm power and responsiveness of the engine.

New Member

Cam duration is a big determining factor in the operating range of a motor. A small duration number favors low rpm operation, while bigger numbers favor high rpm. Above all, the components must be well matched. A big cam may not make the power you want if it is matched with a stock carburetor or small valve head. Duration is often measured at .050 lift (50 thousandths of an inch) this may give a more accurate idea of the camshaft nature when compared to other .050 duration numbers. Some cams have opening rates that are very slow, and can make it look like a big duration cam, when it really isn't.. 050 figures allow the valve to open a bit, and provide a better comparison between cams. All that said, Nelson Racing makes a really good mini bike cam- the 280 series. It has high lift, and short duration. Duration is 220 at .050, lift is .280. It is advertised as the ultimate mini bike cam. It would replace a stock cam, and work with the other stock components. I had one in my built predator, and it ran great. I switched to the black mamba cam which is 245 at .050, and .275 lift. It moved the powerband up to the 4000- 7000 rpm range. Iirc, the NR cam started pulling about 2500, and ran out of suds about 6k. If you can make the same power at a lower rpm, it is much easier on parts. The go cart racing folks have really figured the predator motors out, but with all the rules, it can be hard to find something suitable for a no-rules mini bike. The NR cam is a really good one, imho.